1. Field of the Invention
The present invention relates to a wafer container in which a plurality of wafers made of semiconductor, quartz, or glass are arranged at intervals, and an apparatus for aligning the wafers stored in the container.
2. Description of the Related Art
In a process of manufacturing semiconductor devices, various heat treatments are carried out for oxidation, diffusion, CVD, annealing, etching and so forth. In these steps, a container 2 as shown in FIG. 1 for storing a plurality of wafers at intervals is used to transfer the wafers near a processing apparatus.
The wafer container 2 has a main opening 3 through which wafers W are inserted therein and a sub-opening 4 which is smaller than the main opening 3. The wafers W are approached through the sub-opening 4 by an apparatus for aligning orientation flats OF of the wafers W and counting the number of the wafers W. The aligned orientation flats OF can stay on the side of the sub-opening 4 or moved to the side of the main opening 3.
A number of holding slots 5 for holding the wafers W are formed parallel with one another on the inner surfaces of the container 2. Each slot has a pair of opposing grooves formed on the inner surfaces of the container 2. Each groove has a V-shaped cross-section which divergently opens toward the inside of the container 2 as shown in FIG. 2, so that a wafer can easily be inserted therein. Hence, when the container 2 is placed so as to hold the wafers w substantially horizontally, each wafer w is supported by a tapered supporting surface 6 which corresponds to a side of a V-shaped slot 5. When the container 2 is placed so as to hold the wafers W substantially vertical, each wafer W is supported by both sides of the sub-opening 4 in a state where the side or the edge of the wafer W abuts on the innermost part of the V-shaped slot 5.
However, even if the container having V-shaped slots is placed such that wafers w are supported substantially horizontal, the wafers w cannot be completely horizontal and somewhat slant at various angles. More specifically, when a wafer w is inserted in a slot 5, an edge WE of the wafer W does not reach the innermost part of the groove at a position shown in FIG. 4A, which shows a cross section taken along the line IVA--IVA in FIG. 3, since a clearance 7 of about 1 to 2 mm is provided in this position to easily insert or withdraw the wafer W into or from the slot. In contrast, at a position shown in FIG. 4B, which shows a cross section taken along the line IVB--IVB in FIG. 3, the edge WE of the wafer W reaches the innermost part of the groove. For this reason, the upper surface of the wafer W, which has an uniform thickness, is located at a level L1 in the position corresponding to the line IVB--IVB and below the level L1 in the position corresponding to the line IVA--IVA. In short, the wafer W slants to the main opening 3 slightly downward as shown in FIG. 5A. FIG. 5A is an emphasized view in which the ratio of the height to the width is about ten times larger than the real. Although the wafers W are shown to partly overlap with projecting portions of container 2 which are shown with hatching in FIG. 5A, the wafers have an outline or width in a plan view, which becomes narrower gradually toward the main opening 3 of the container 2, and thus do not interfere with any part of the slots 5.
In the inclined state as described above, when an arm 8 (FIGS. 6A and 6B) for transferring wafers W is inserted between two wafers, an end of the arm 8 may be in contact with the wafers and damage them. When the slot 5 is slanted to make the wafers w more horizontal, as shown in FIG. 5B, the wafers tend to be brought into contact with the ceiling surfaces of the slots 5, resulting in damage of the wafers.
Further, the front edges of wafers W stored in the container 2 are not completely aligned, as shown in FIGS. 6A and 6B, due to less accurate dimensions in manufacturing the container 2. This positional variation of wafers W occurs particularly when the container 2 is rotated from a substantially vertical state to a substantially horizontal state. The positional variation causes misarrangement of wafers when the wafer W are transferred to a wafer boat or the like.
The larger the size (6 inches or 8 inches) of the wafers, the more serious the above problem.